The invention relates to a system or an arrangement for centering information discs. The system comprises drive units as well as interchangeable information discs which are adapted to be placed into the drive units and to be removed therefrom. The discs are each provided with a carrier and an information layer supported thereby, as well as a central opening which is defined by an inner wall, a centering device being provided for centering the information disc in each drive unit. The system comprises: a turntable rotatable about an axis of rotation, which turntable has a supporting surface for an information disc on one end, in which a recess is formed defined by an inner wall which is coaxial with the axis of rotation; a centering element which rotates with an information disc, the element including a central portion, elastic portions which extend at least substantially radially and, near the ends thereof, transverse portions adapted for engagement both with the inner wall of the central opening of the information disc and with the inner wall of the recess in the turntable, for centering the information disc on the turntable in response to elastic axial displacement of the central portion; as well as displacement means in the drive unit for axially displacing the central portion of the centering element.
Systems of the forementioned type (for example known from U.S. Pat. No. 4,125,883), using inexpensive, flexible information discs manufactured from magnetic foil, are employed in various fields of data processing. The information disc in accommodated in a special enclosure in the form of a square envelope which is formed with a slot via which one or more magnetic heads have access to the information disc and with a central opening which is larger than the central opening in the information disc itself, so that a portion of the information disc around its central opening is accessible from the exterior of the enclosure.
Drive units for such disc units are commercially available and have gained a certain popularity because of their small dimensions and comparatively low cost. They are for example used for the storage of data or programs for small computers and similar equipment, such as for example text processors. The flexible information disc is rotated inside its enclosure with a comparatively low speed, for example, 300 revolutions per minute. The centering quality of the information disc on the turntable is determined by the difference between the dia-meter of the central opening in the information disc and the diameter of the recess in the turntable. As a standard the information discs are formed with a central opening having a diameter which is slightly greater than that of the recess in the turntable. Deviations from this standard diameter, within a comparatively large tolerance range, are considered to be permissible. A certain eccentricity of the information disc on the turntable is therefore inevitable. However, for the relevant purpose, this is considered to be acceptable because the flexible information discs are not intended for those applications wherein very large amounts of data are to be packed very densely on the disc. Furthermore, the information discs have such a low mass that at the low rotational speed they produce such low centrifugal forces that the resulting eccentricity will not always be equal to the maximum possible eccentricity. The frictional forces occurring between the turntable and the information disc are sufficiently great to prevent shifting of the information disc under the influence of the centrifugal forces which are produced.
There has been a long felt need for arrangements which, similarly to the flexible information disc systems, have a broad field of application and furthermore have small dimensions, but which in addition are suitable for the storage and reproduction of substantially greater amounts of data. In such systems the requirements imposed upon the maximum permissible eccentricity of the information disc are more stringent. Thus, it is no longer possible to employ systems in which a maximum eccentricity of the information disc relative to the axis of rotation of the turntable can occur which is equal to the difference between the diameter of the central opening in the information disc and the recess in the turntable.